Cathodic protection system and delay-activation anode

ABSTRACT

THE SPECIFICATION DISCLOSED AN EXTENDED LIFETIME CATHODIC PROTECTION SYSTEM EMPLOYING SEQUENTIALLY ACTIVATED GALVANIC ANODES. ALL OF THE ANODES ARE CONNECTED BY MEANS OF AN ELECTRICAL CONDUCTOR TO THE METALLIC STRUCTURE TO BE PROTECTED SO THAT AS ONE ANODE IS CONSUMED AN ADDITIONAL ANODE OR ANODES ARE ACTIVATED IN SEQUENCE TO PROVIDE CONTINUOUS ELECTRICAL CURRENT FLOW OVER ANY DESIRED PERIOD OF TIME. A DELAY-ACTIVATION ANODE IS DISCLOSED WITH A BODY OF ANODE MATERIAL ENCLOSED BY A HERMETIC CASING WHICH INCLUDES A RELATIVELY CORRODIBLE MATERIAL SUCH AS IRON. THE CORRODIBLE MATERIAL IS CHOSEN TO PROVIDE A PREDETERMINED CORROSION RATE WHEN IMMERSED IN A PARTICULAR ELEC-   TROLYTE, WHEREBY AN OPENING IS CREATED TO EXPOSE THE ANODE MATERIAL AT A DESIRED DELAY TIME.

Stpt. 5, 1972 v BLOUNT ET AL 3,589,395

CATHODIC PROTECTION SYSTEM AND DELAY-ACTIVATION ANQDE Filed June 20.1969 PIPELINE GALVANIC ANQDES ifi LI] ghs h,

FIG.2

72 FLOYD E. BLOUNT WALLACE B. ALLEN INVENTORS 70 BY 13mm ATTORNEY FIG.4

Patented Sept. 5, 1972 4 Claims ABSTRACT OF THE DISCLOSURE Thespecification discloses an extended lifetime cathodic protection systememploying sequentially activated galvanic anodes. All of the anodes areconnected by means of an electrical conductor to the metallic structureto be protected so that as one anode is consumed an additional anode oranodes are activated in sequence to provide continuous electricalcurrent flow over any desired period of time. A delay-activation anodeis disclosed with a body of anode material enclosed by a hermetic casingwhich includes a relatively corrodible material such as iron. Thecorrodible material is chosen to provide a predetermined corrosion ratewhen immersed in a particular electrolyte, whereby an opening is createdto expose the anode material at a desired delay time.

BACKGROUND OF THE INVENTION This invention relates to a novel method andapparatus for cathodic protection of metallic structures and, moreparticularly, to a delay-activation galvanic anode and process formaking the same.

It is well known that a metallic structure, such as a pipeline, whenburied in the ground or immersed in a body of water, is subject tocorrosion by galvanic action with the ground or water-forming anelectrolyte. A techniquecalled cathodic protection has been used forreducing the corrosion rate of such metallic structures, by making thesteady state or corrosion electrical potentials of the metallicstructure more electronegative. The method is normally-applied to ironor steel structures but it is also used for lead, aluminum, and othermetalcontaining structures. An exposition on cathodic protection isfound in Fundamentals of Cathodic Protection by F. E. Blount, Universityof Oklahoma Corrosion Control Short Course, Proceedings pages C-1C2'9,1968.

In cathodic protection, galvanic anodes, constructed of some materialsuch as magnesium or zinc, are located in the same electrolyte with ametallic structure and are connected by means of an electrical conductorto such structure. Corrosion occurs at the galvanic anodes instead of atthe structure being protected. Consequently, when complete consumptionof the galvanic anode occurs, the lifetime of the cathodic protectionsystem ceases. Normally, groups of galvanic anodes are connected inseries by a single electrical conductor to the metallic structure beingprotected. These galvanic anodes are activated when first located in theelectrolyte and all become consumed at essentially the same time. Thelifetime of a cathodic protection system depends on various factorsincluding the anode-to-electrolyte resistivity, but the maximum lifetimeordinarily expected for any environment is about ten years.

SUMMARY OF THE INVENTION This invention provides a novel method andapparatus for providing extended lifetime cathodic protection for ametallic structure located in an electrolyte. The method comprisesinserting a plurality of galvanic anodes into the electrolyte, eachanode being adapted to be activated sequentially. All of these anodesare connected by means of an electrical conductor to the metallicstructure to be protected, whereby as one galvanic anode is consumed, anadditional anode or anodes are activated in sequence to providecontinuous electrical current flow through the conductor connected tothe metallic structure. Any desired number of galvanic anodes can bearranged to be adapted at the same time to provide the desired currentdensity for the cathodic protection system.

By another feature of the present invention, there is provided adelay-activation galvanic anode and process for making the same. Theprocess comprises the steps of securing an electrical lead to a body ofanode material, such as magnesium, and bonding a piece of corrodiblematerial to the edge of the body of anode material. This piece ofcorrodible material, e.g., iron, is chosen to provide a predeterminedcorrosion rate when immersed in an intended electrolyte, whereby apassageway will be corroded through the piece of corrodible material toexpose the body of anode material to the electrolyte. The portion of thebody of anode material which surrounds the piece of corrodible materialis coated with a coating material which is substantially impervious tocorrosive action, thereby providing a hermetic casing around the anodematerial.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be furtherdescribed with reference to certain specific embodiments thereof and theaccompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a cathodic protectionsystem illustrating the present invention in connection with a pipelineunderlying a body of water;

FIG. 2 is an elevational view of one type of delayactivation galvanicanode;

FIG. 3 is a sectional view taken along line 33 in FIG. 2; and

FIG. 4 is a sectional view taken along line 44 in FIG. 2.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring more specifically to thedrawings, FIG. 1 illustrates the present invention embodied in acathodic protection system for a pipeline 10 lying on or embedded inmarine bottom 11 beneath the surface of a body of water 12. The cathodicprotection system comprises a plurality of galvanic anodes lying onmarine bottom 11 at some distance from the pipeline 10. It will beappreciated that the elements of a cathodic protection system are shownschematically and that in an actual embodiment of the invention theusual practices and components of a cathodic protection system will beprovided.

The galvanic anodes 14a-14e are connected by an electrical conductor 16to a terminal 18 on the pipeline 10. Galvanic anodes 14a-14e arearranged to be activated sequentially. More particularly, when firstlocated in the water the galvanic anode 14a is arranged to be activatedimmediately to begin providing galvanic current through the conductor 16to provide cathodic protection for pipeline 10. The anodes 14b-14c areadapted to have delayedactivation times so that they become activatedafter the initial anode 14a has been substantially consumed. Forexample, anode 14b may have a delay time of two years, anode 14c fouryears, anode 14d six years, and anode 14c eight years. Accordingly,anodes 14b-14c will be activated sequentially so that only after eightyears of operation will the anode 14e become activated.

FIGS. 2-4 illustrate one type of delay-activation galvanic anode whichcan be used in the cathodic protection system described in connectionwith FIG. 1. It will be appreciated that the galvanic anode has aspecific shape illustrated which may be varied to fit the particularapplication required. It will also be appreciated that the galvanicanode assembly may have additional uses besides the cathodic protectionsystem described above; for example, as an element of an electricalpower source as dc scribed in copending application Ser. No. 835,022 tothe present inventors, filed on June 20, 1969, now US. Pat. No.3,568,140, entitled Underwater Electrical Power Source and Sonic Beacon.

The galvanic anode illustrated comprises a body of anode material 70,such as magnesium, which is encased by a coating 72 of a suitablematerial such as plastic, which is substantially impervious to corrosiveaction in the electrolyte intended for use. A plug or plate 74 of somecorrodible material, such as iron, forms a closure for an opening in thecasing or coating 72. The thickness, size, and properties of the plug 74are chosen so as to provide a predetermined rate of corrosion whenexposed to an electrolyte intended to be used. For example, in order toprovide a delay activation of two years, a plate of iron on the order ofone-fourth inch thick may be used for an electrolyte of sea water.

Embedded in the body of anode material 70 is a metallic core or rod 78which provides an electrical terminal for the galvanic anode.

One process for manufacturing the delay-activation galvanic anodeassembly shown in FIGS. 24 comprises casting the body of anode material70 around the metallic core 78 in any desired molding shape. The plate74 of corrodible material can then be cast in the recess formed in theside of the body of anode material 70 as shown in FIGS. 2-4. The casingfor hermetically sealing the galvanic anode assembly can be formed bycoating the body of anode material 70 with a coating material 72 ofplastic material such as polyvinylchloride. The coating material can beapplied to all the portions of the body of anode material 70 except thecorrodible plug 74, which remains exposed to the exterior.

The invention claimed is:

1. A cathodic protection system for a metallic structure located in anelectrolyte comprising:

a plurality of galvanic anodes located in said electrolyte,

each of said galvanic anodes comprising:

a body of anode material;

an electrical lead secured to said body of anode material;

a casing surrounding said body of anode material and said electricallead, said casing being impervious to corrosion and having at least oneopening; and

a means for actuating said anode at a difierent time with respect to theothers of said plurality of anodes, said actuating means comprising aclosure means sealed in said opening, said closure means being of acorrodible material and having 4 properties such that corrosion of apassageway through said closure means will occur at a predetermined timeafter said galvanic anode is exposed to said electrolyte; and

electrical connector means for connecting each of said plurality of saidanodes to said metallic structure whereby said plurality of galvanicanodes may be sequentially activated to provide extended-life cathodicprotection for said metallic structure.

2. A cathodic protection system as defined in claim 1 wherein saidcasing comprises a coating of plastic material on said body of anodematerial.

3. A cathodic protection system as defined in claim 1 wherein saidclosure comprises a plate secured to the exterior of said body of anodematerial.

4. A cathodic protection system for a metallic structure located in anelectrolyte comprising:

a plurality of galvanic anodes located in said electrolyte,

each of said galvanic anodes comprising:

a body of anode material;

an electrical lead secured to said body of anode material; and

a hermetic casing enclosing said body of anode material, at least aportion of said casing comprising a corrodible material exposed to theexterior thereof, whereby said anode body may become exposed to anelectrolyte at a delayed time after location therein; and

electrical connector means for connecting each of said plurality of saidanodes to said metallic structure whereby said plurality of galvanicanodes may be sequentially activated to provide extended-life cath-odicprotection for said metallic structure.

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